1. Field of the Invention
The present invention relates to a Passive Optical Network (PON), and more particularly to a Time-Division-Multiplexed (TDM) PON.
2. Description of the Related Art
In a TDM PON, multiple subscribers share a single wavelength. According to a static bandwidth allocation method, an Optical Line Terminal (OLT) statically allocates one time slot obtained by dividing one cycle to each subscriber. Each subscriber can transmit upstream optical signals to the OLT only during the allocated time slot. According to a dynamic bandwidth allocation method, the following steps are performed:
(1) an OLT transmits a message (information request message) requesting information about a required bandwidth to all Optical Network Units (ONUs);
(2) each of the ONUs having received the corresponding information request message transmits a message (bandwidth request message) including the information about the required bandwidth to the OLT;
(3) the OLT receives the bandwidth request messages from all of the ONUs, allocates a corresponding time slot within one cycle to each of the ONUs according to a preset bandwidth allocation algorithm, and transmits a message (bandwidth allocation information message) including information about the corresponding time slot to each of the ONUs;
(4) each of the ONUs having received the corresponding bandwidth allocation information message transmits upstream optical signals to the OLT during the allocated time slot; and
(5) steps (1) to (4) are repeated in a cycle-by-cycle basis.
However, the TDM PON performing the dynamic bandwidth allocation method as described above has the following problems:
First, continuously performing steps (1) to (3) unnecessarily utilizes resources within the OLT resulting in a deterioration of service quality, for example, in services requiring realtime transmission; and
Second, the OLT must have a complex processor for performing steps (1) to (3), which results in an increase in the cost required to construct the OLT.